There has heretofore been known a magnetic disk device of the ramp loading type, i.e., a magnetic disk device of the dynamic loading/unloading type, which is a version of the so-called non-contact start-stop (N-CSS) system in which a magnetic head is held out of contact with a disk. Such a magnetic disk device is arranged as shown in FIG. 1 of the accompanying drawings.
As shown in FIG. 1, a magnetic disk device 1 includes a magnetic disk 2 which can be rotated and an actuator 3 which supports a head slider for movement in a slightly floating condition radially over the surface of the magnetic disk 2.
The actuator 3 comprises an arm 5 supported for rotation about a rotational shaft 4, a head slider 7 supported on a distal end of the arm 5 by a suspension 6, and a voice coil motor having a voice coil 8 for rotating the arm 5 about the rotational shaft 4.
The head slider 7 has a magnetic head (not shown).
The magnetic disk device 1 also includes a cam follower 6a extending from a distal end of the suspension 6, and a cam 9 disposed in the vicinity of an outer circumferential edge of the magnetic disk 2. These components make up a loading and unloading apparatus.
With the magnetic disk device 1 thus arranged, the head slider 7 is kept slightly floated off the surface of the magnetic disk 2 which is rotating.
When the arm 5 is rotated about the rotational shaft 4, the head slider 7 moves radially over the surface of the magnetic disk 2 thereby accessing tracks positioned circumferentially on the magnetic disk 2.
When the magnetic disk device 1 starts and stops operating, loading and unloading operations are carried out as follows:
In the loading operation, the arm 5 is turned about the rotational shaft 4 by the voice coil 8 to move the cam follower 6a radially inwardly of the magnetic disk 2, i.e., in the direction indicated by the arrow R1 from a parking area 9a of the cam 9.
As the arm 5 is turned, therefore, the head slider 7 is lifted over the magnetic disk 2 and thereafter lowered along a cam surface 9b of the cam into a position near the surface of the magnetic disk 2.
In the unloading operation, the arm 5 is turned about the rotational shaft 4 by the voice coil 8 to move the cam follower 6a radially outwardly of the magnetic disk 2. While the cam follower 6a is being held in abutment against the cam surface 9b, which is a slanted surface, of the cam 9, the cam follower 6a is lifted and moved in the direction indicated by the arrow R2 toward the parking area 9a.
As the arm 5 is turned, therefore, the head slider 7 is moved away from the surface of the magnetic disk 2, and thereafter lifted along the cam surface 9b of the cam 9. Subsequently, the head slider 7 is carried onto the parking area 9a of the cam 9.
The loading speed is generally given as a considerably high speed for enabling the head slider 7 to move from the parking area 9a onto the magnetic disk 2 against the resistance due to the friction between the cam follower 6a and the cam 9.
The unloading speed is generally given also as a considerably high speed for enabling the head slider 7 to move from the magnetic disk 2 onto the parking area 9a against the resistance due to the friction between the cam follower 6a and the cam 9.
In case of emergency such as a power failure while the head slider 7 is floating, the magnetic disk device 1 unloads the head slider 7 to retract the same. The unloading speed at this time (the unloading speed at the time the head slider 7 is retracted will hereinafter be referred to as a "retracting speed") is generally given as a considerably high speed. The retraction is an Unloading action in case of emergency.
A magnetic disk device of the so-called contact start-stop (CSS) configuration in which a magnetic head is held in contact with a disk is arranged as shown in FIG. 2 of the accompanying drawings. Those parts in FIG. 2 which are identical to those shown in FIG. 1 are denoted by identical reference characters, and will not be described in detail below.
As shown in FIG. 2, a magnetic disk device 1a has a CSS zone CSS in a retraction area in a radially inner region of a magnetic disk 2a, the retraction area being outside of a data area. The magnetic disk device 1a also has a stopper 3c for mechanically stopping operation of an actuator 3a to stop movement of a head slider 7 radially inwardly of the magnetic disk 2a at the CSS zone CSS.
With the magnetic disk device 1a, the head slider 7 is kept slightly floated off the surface of the magnetic disk 2a which is rotating. When the arm 5 is rotated about the rotational shaft 4, the head slider 7 is moved radially over the surface of the magnetic disk 2a to access tracks on the magnetic disk 2a.
When the magnetic disk device 1a starts and stops operating, loading and unloading operation are carried out. In loading operation, when the magnetic disk 2a is rotated with the head slider 7 held in the CSS zone CSS, the head slider 7 is floated off the magnetic disk 2a, and then when the arm 5 is turned about the rotational shaft 4 by the voice coil 8, the head slider 7 is moved radially outwardly of the magnetic disk 2a toward the data zone in the direction indicated by the arrow R2.
In the unloading operation, when the arm 5 is turned about the rotational shaft 4 by the voice coil 8, the head slider 7 is moved radially inwardly of the magnetic disk 2a in the direction indicated by the arrow R1. Abutment of the actuator 3a against the stopper 3c stops the angular movement of the arm 5, whereupon the magnetic disk 2a stops its rotation.
Therefore, as the arm 5 is turned, the head slider 7 is carried into the CSS zone CSS while floating off the surface of the magnetic disk 2. When the magnetic disk 2a is stopped against rotation, the head slider 7 is brought into and held in contact with the CSS zone CSS.
In the event of an emergency such as a power failure while the head slider is floating, the head slider 7 is unloaded or retracted at a retraction speed which is generally considerably high.
The actuators 3, 3a of the magnetic disk devices comprise a source of magnetic fluxes such as a permanent magnet and a voice coil motor. In the conventional loading/unloading apparatus, the speed at which the actuators 3, 3a are driven, i.e., the speed at which the head slider 7 is loaded and unloaded, is generally not controlled, or not adjusted to a desirable speed.
Therefore, when the head slider 7 is loaded onto or unloaded from the magnetic disks 2, 2a, the head slider 7 tends to collide with the magnetic disks 2, 2a.
In the magnetic disk device of the dynamic loading/unloading type, the speed at which the head slider 7 moves vertically toward and away from the surface of the magnetic disk 2 is calculated by converting the angular velocity at which the actuator 3 rotates along the surface of the magnetic disk 2 clockwise or counterclockwise in a .theta. direction about the rotational shaft 4, i.e., the speed at which the head slider 7 moves in the direction R1 or R2, at a certain ratio that is determined by the angle of inclination of the cam surface 9b, which is a ramp, of the cam 9.
The relationship between the speeds of the head slider 7 in the vertical directions when the head slider 7 is loaded and unloaded, i.e., the loading and unloading speeds, and the magnitudes of shocks produced when the head slider 7 collides with the surface of the magnetic disk 2 is illustrated in a graph shown in FIG. 3 of the accompanying drawings.
The magnitudes of shocks plotted in the graph are represented as output voltages from an AE sensor. A study of FIG. 3 indicates that as the loading and unloading speeds increase, the shocks produced when the head slider 7 collides with the magnetic disk 2 increase.
FIG. 4 of the accompanying drawings shows the relationship between the speed of the head slider 7 in a horizontal direction when the head slider 7 is retracted, i.e., the retracting speed, and the magnitudes of shocks produced when the head slider 7 collides with the surface of the magnetic disk 2, the magnitudes of shocks being detected by an AE sensor. It can be seen from FIG. 4 that as the retracting speed increases, the shocks produced by collisions between the head slider 7 and the magnetic disk 2 also increase.
In the magnetic disk device of the CSS system, when the head slider is unloaded, the actuator 3a collides with the stopper 3c, and then the head slider 7 collides with the magnetic disk 2a due to shocks produced by the collision between the actuator 3a and the stopper 3c. As the unloading speed increases, the shocks produced by the collision between the head slider 7 and the magnetic disk 2a increase.
When the shocks produced by the collision between the head slider 7 and the magnetic disks 2, 2a increase, the head slider 7 may be broken and the surfaces of the magnetic disks 2, 2a may be damaged.
Since various data are recorded as magnetic information on the magnetic disks 2, 2a, any damage to the surfaces of the magnetic disks 2, 2a may possibly result in a failure to read the magnetic information therefrom.
In the retracting operation, the retracting speed needs to be higher because the head slider 7 is retracted in case of emergency. The higher retracting speed causes larger shocks to be produced by the collision, resulting in a greater danger of damage.
In view of the above shortcomings, it is an object of the present invention to provide a loading and unloading apparatus for controlling loading and unloading speeds and positions, including those upon retraction, so as to be of desired values, to avoid collisions between a head and a disk as much as possible to allow the head to read recorded information safely from the disk.
In a magnetic disk device of the N-CSS type, a magnetic head slider with a magnetic head mounted thereon is held out of contact with a disk. Therefore, no positional or speed information can be read from the disk when the head slider starts being loaded, i.e., moving from a retracted position, and also when the head slider starts being unloaded, i.e., returning from a data zone to the retracted position.
Therefore, the principles of the present invention are applicable to a magnetic disk device of the N-CSS type when the head slider is retracted due to a power failure or the like, loaded, and unloaded.
In a magnetic disk device of the CSS type, when a disk starts rotating while a head is held in contact with the disk, a head slider floats off the disk, and can immediately read positional or speed information from the disk. When the head slider is unloaded, positional or speed information can be read from the disk after the rotation of the disk has stopped until the head slider contacts the disk. Therefore, the principles of the present invention are not applicable to a magnetic disk device of the CSS type when the head slider is loaded and unloaded except where disk surface information is not recorded in the retraction zone (CSS zone), but applicable only when the head slider is retracted in case of emergency, i.e., retracted, at the time the power supply is shut off and no information can be read from the disk.